1. Field of the Invention
The present invention relates to an apparatus for recording or reproducing information, and an information recording medium for use therein.
2. Related Background Art
Recently developed scanning tunnel microscope (hereinafter called STM) for directly observing electron structure on the surface of a material or in the vicinity of the surface, as disclosed by G. Binning et al., Helvetica Physica Acta, 55, 726 (1982), allows measurement of real space image with a high resolving power, regardless whether said material is monocrystalline or amorphous. Various applications are anticipated because of the advantages that the observation can be conducted with a low electric power without damage to the object by electric current, and that said microscope is usable not only in ultra high vacuum but also in the air or in solution and for various materials.
Also there have been developed information record/reproducing apparatus utilizing such scanning tunnel microscope, as disclosed in the Japanese Laid-open Patents Sho 63-161552 and Sho 63-161553.
Such known record/reproducing apparatus has a structure as shown in FIG. 1.
In such apparatus, a DC voltage is given a recording medium 8 so as to generate a tunnel current by means of a voltage applying unit 5, and the distance between a probe electrode 6 and said recording medium 8 is so controlled as to obtain a constant tunnel current. A pulse voltage is given across the recording medium 8 having a switching memory effect for forming a local area of different electric resistance at a desired recording position.
At the reproducing operation, the distance between the probe electrode 6 and the recording layer is controlled at a constant value, under the application of a small voltage, by means of a current amplifier 7, a servo circuit 3 and a three-dimensional driving mechanism 2. The surface of the recording medium is scanned by an X-Y scanning drive circuit 4 and the three-dimensional driving mechanism 2 while the probe electrode 6 runs on said surface so as to provide a constant detection current, and the recorded information is reproduced on the basis of both the Z-axis control amount corresponding to the difference in electric resistance formed in the recording operation and the position of the probe electrode on said surface. Such controls are conducted by a microcomputer 1. Since the tunnel current starts to flow only when the distance between the probe electrode 6 and the recording medium 8 becomes as small as about 1 nm, highly precise manufacturing technology is required for the control mechanisms for said probe electrode 6 and recording medium 8. In FIG. 1 there are further shown a base electrode 9, a substrate 10, a coarse moving mechanism 11, a coarse driving circuit 12, and an X-Y stage 13.
In such conventional record/reproducing apparatus, the surface of the recording medium and that of the probe electrode are exposed to the air. Consequently, the eventualy deterioration of said surfaces caused by the moisture or oxygen in the air gives rise to errors in information reproduction and significant deterioration in S/N ratio. Also the surface of the recording medium may be damaged or smeared by the dusts in the air, eventually causing errors in the information recording or reproduction.